I want to get a 'fast' lens, and ideally a cheap(er) one that would work with the D5000 (lack of) auto focus.

My two other lenses are the kit ones: 18-55 and a 55-200, I'm looking to shoot in low light without flash and especially kids jumping around... so need a fast lens, pelase advise, it doens't have to be a Nikkor one,